The present invention concerns total hip prostheses and relates more particularly to prostheses which require fitting of a device intended to restore an acetabular cavity of the iliac bone which has been damaged, in particular due to arthrosis, with a view to being able to receive the head of a femoral prosthesis.
In order to restore an acetabular cavity, it is customary to put a prosthetic acetabulum in place and to fix it either by cement or by impaction or with the aid of suitable screws.
However, exact orientation of the acetabulum to be implanted in the acetabular cavity as a function of the orientation of the joint to be restored is very delicate insofar as the anatomical references are not reliable.
This entails risks of error in the orientation of the acetabulum, and these can lead to poor orientation of the prosthetic joint, with risks of luxation of the prosthesis.
The invention aims to remedy the disadvantages of the prior art by making available an implantable acetabulum with which it is possible to choose a correct orientation of the prosthetic acetabular cavity.
The subject of the invention is therefore a trial acetabulum or implantable acetabulum comprising a hemispherical cup intended to be placed in an acetabular cavity, and a hemispherical insert of biocompatible plastic intended to be engaged concentrically in said cup, characterized in that it additionally comprises an external cap in the form of a spherical dish provided with pins for anchoring in the bone of the acetabular cavity and intended to receive the cup, an internal plate intended to be placed in the cup opposite the external cap and connection means for connecting the external cap and the internal plate, the cap and the plate defining means for adjusting the angular position of the cup in the acetabular cavity as a function of the orientation to be given to the joint, while the means for connecting the external cap to the internal plate include means for immobilizing the cup relative to the external cap after the angular position of said cup has been adjusted.
According to other characteristics of the invention:
the external cap includes a threaded centering sleeve, which protrudes inward and is intended to cooperate with an external centering collar provided on the internal plate, the sleeve and the collar guiding the translational movement of the internal plate relative to the external cap, a tightening screw which is intended to be engaged in the threaded sleeve of the external cap and whose frustoconical head cooperates with a seat of corresponding shape formed in the internal plate and coaxial to said collar forming, with the threaded sleeve of the external cap and the collar of the internal plate, said means for connecting the cap to the plate;
the hemispherical cup includes a central orifice traversed by the means for connecting the external cap to the internal plate, with a clearance which allows the angular position of the cup to be adjusted relative to the cap in all directions;
the hemispherical insert is a trial insert which includes a central orifice for access to the screw for connecting the external cap to the internal plate;
the insert is a complete and final hemispherical insert which can replace the trial insert upon completion of the operation of orienting and immobilizing the cup relative to the external cap;
the cup comprises an external zone of reduced thickness for receiving the external cap in such a way as to present, together with the external cap, an almost continuous external surface;
the cup has, in its internal wall, a thinned wall portion receiving the internal plate;
the angular extent of the external zone receiving the external cap and the angular extent of the internal wall portion receiving the internal plate are greater than the angular extents of the cap and of the plate by a value corresponding at least to the variation to obtain in the angular orientation of the cup relative to the external cap and to the internal plate.
the head of the screw has a concave end surface, while the summit of the final insert has a recess which is intended to prevent the summit of said insert from abutting against the head of the screw.